I have a 1980 model with a professionially rebuilt carb per the previous owner. Bought it with the running issue described in thread title. I pulled the carb, checked the rubber/metal carb to head spigot for possible cracking/leaks, checked the main and pilot jets for obstruction, and reinstalled with a fresh gasket between the spigot and head.

It will start easily with choke and as it warms, the choke can be decreased to about 75% off but no more, it will die. Trying to rev it while pushing the choke to completely off doesn't work, it will die, even when warm. I take this to mean it is getting too much air. Should I experiment with the air pilot adjustment? It is located downstream of the slide. It is currently 2 turns out from all the way in.

I confirmed it has the correct main jet but I didn't check the needle position. The accelerator pump works. I don't know if the float level is correct and it might be the last thing to check anyway.

too much air could also means not enough fuel: Its a ratio kind of thing. So before going further think about where fuel could be blocked, rather than how too much air could get in.

So since you cleaned everything, and checked for blockages, I would start playing with that pilot. bring it out a half turn, most people do that anyway during the winter months. See if you get any change at all. If you do then you know somewhere to start.

Throw a new plug in there too... never know if it maybe is fouled from running lean or just plain is old and dirty.

too much air could also means not enough fuel: Its a ratio kind of thing. So before going further think about where fuel could be blocked, rather than how too much air could get in.

So since you cleaned everything, and checked for blockages, I would start playing with that pilot. bring it out a half turn, most people do that anyway during the winter months. See if you get any change at all. If you do then you know somewhere to start.

Throw a new plug in there too... never know if it maybe is fouled from running lean or just plain is old and dirty.

Thanks, that was in the back of my mind, not enough fuel. The float could be misadjusted, shutting off fuel to the bowl way too soon. Plug looked good, correct gap. Starts easily with choke on but I have heard other stories of running issues unexpectedly resolved via new plug. Will play with the pilot tomorrow.

That's typical of a plugged up pilot jet. Maybe the "professional" who rebuilt the carb missed it.

And it could be that the jet is clear, but there is crap in the transition slot/port(s).

There was mention of an idle air screw. Is there also an idle mixture (fuel) screw that's maybe not open far enough? Also, will it take throttle with the choke/enrichener engaged, or does it always die when you give it gas, regardless of choke setting?

The first thing I would check is the float level, because that changes the behavior of every other fuel circuit in the carb.

And it could be that the jet is clear, but there is crap in the transition slot/port(s).

There was mention of an idle air screw. Is there also an idle mixture (fuel) screw that's maybe not open far enough? Also, will it take throttle with the choke/enrichener engaged, or does it always die when you give it gas, regardless of choke setting?

The first thing I would check is the float level, because that changes the behavior of every other fuel circuit in the carb.

Float level doesn't really affect the idle circuit as much because the fuel comes from much lower in the bowl. The fact that it won't idle without fuel from the enrichener tells me that it's not getting much if any from the idle circuit.

And it could be that the jet is clear, but there is crap in the transition slot/port(s).

There was mention of an idle air screw. Is there also an idle mixture (fuel) screw that's maybe not open far enough? Also, will it take throttle with the choke/enrichener engaged, or does it always die when you give it gas, regardless of choke setting?

The first thing I would check is the float level, because that changes the behavior of every other fuel circuit in the carb.

I can rev it with the choke on or 50% on. There is no idle mixture screw although I guess the air pilot contributes to idle mixture. There was a small amount of crap in the bowl. I will try different pilot adjustments and if that doesn't help, out comes the carb again.

I'd be willing to bet that you do have an idle mixture screw, but it's hidden under an aluminum plug/cover, courtesy of the EPA. I usually drill through the plug, use a sheet-metal screw to remove it. Then determine the position of the mixture screw, remove it, blow solvent then air through the passage. Replace the screw with the o-ring, backing washer, spring. Remember to also clean off the screw tip.

I can rev it with the choke on or 50% on. There is no idle mixture screw although I guess the air pilot contributes to idle mixture. There was a small amount of crap in the bowl. I will try different pilot adjustments and if that doesn't help, out comes the carb again.

If that doesn't work out for you let me know. I can put it in my ultrasonic cleaner and if there is any plugged passages it will clean them up.